(1) Field Of The Invention
The present invention generally relates to corrosion inhibiting compositions, and more particularly to corrosion inhibiting coating compositions that employ blends of an intrinsically conducting polymer and an adhesive polymer.
(2) Description Of The Related Art
Corrosion is a problem associated with virtually all metal objects that are exposed to the environment or subjected to harsh environmental conditions. The effects of corrosion are particularly noticeable in automobiles, ships, aircraft, heavy machinery and bridges. Corrosion is also problematic in the road construction industry, various industrial processes and the medical industry.
Metal that is, exposed to harsh environmental conditions, such as a high salt concentration or an acidic or basic environment, is subject to the corrosive effects of the environment which, after prolonged or extreme exposure, can cause a breakdown of the metal and compromise its structural integrity. Various corrosion inhibiting compositions have been developed to inhibit the effects of corrosion. Conventional corrosion resistant compositions employ a protective coating that is applied onto the exposed surfaces of the metal object which serves to provide a barrier to environmental attack. The protective coating is typically composed of a synthetic resin or inorganic silicate polymer which provides a continuous coating that will resist corrosive industrial or environmental conditions. Of course, it is essential that the protective coating be capable of adhering to the metal surface. Examples of corrosion inhibiting compositions include polymeric coatings, such as epoxies, acrylics and lacquers, and conventional primers or paints. The coating can comprise simply the polymeric composition or it can include corrosion inhibiting compounds together with the polymer to provide further corrosion resistance. Numerous non-polymeric corrosion inhibiting compositions are known and disclosed, for example, in U.S. Pat. No. 5,152,929 which discloses novel thio(cyclo)alkanepolycarboxylic acids containing heterocyclic substituents, U.S. Pat. No. 4,818,777 which discloses phenolic corrosion inhibitors for coating materials, U.S. Pat. No. 5,098,938 which discloses a multi-component coating composition, U.S. Pat. No. 5,021,489 which discloses a multi-component corrosion inhibiting coating composition, and U.S. Pat. No. 5,183,842 which discloses corrosion resistant surface coatings.
The application of a corrosion inhibiting coating onto a metal object is, however, not a complete solution to corrosion because most coatings are subject to cracks, chips, or scratches which expose the bare metal to the corrosive environment. Even the existence of pinhole size discontinuities in a coating can be problematic. It has been observed that the effects of corrosion at discrete locations as a result of a chip or a scratch can be particularly severe because the effects of the corrosive elements are concentrated at the point of exposure. Accordingly, conventional corrosion inhibiting compositions are not completely satisfactory in providing corrosion resistance to metal objects.
Intrinsically conducting polymers (ICP), organic polymers that have poly-conjugated .pi.-electron systems, have been proposed as potential corrosion inhibiting compositions for metals. Such polymers have not heretofore been considered suitable as protective coatings because of the intractable nature of the intrinsically conducting polymers. That is, the class of ICPs lack the necessary properties, such as adherence, processability and stability, to be acceptable for use as a protective coating on a metal object. Others have attempted to improve the processability of ICPs by blending them with thermoplastic polymers, such as described in European Patent Application No. 0 497 514 A1, or by sulfonating the ICP as described in U.S. Pat. No. 5,109,070. Recently, a report has also been published disclosing the use of a layer of a functionalized ICP, neat polyaniline, overcoated with an epoxy layer to protect steel from corrosion. This report did not address the problem of the lack of adherence properties of the intrinsically conducting polymer and the performance of the coating composition disclosed is inconclusive. To be commercially useful as a protective coating, it is necessary that the ICP be able to adhere to a metal surface while maintaining its corrosion inhibiting properties.
Therefore, a substantial need exists for a means to utilize ICPs in a coating composition for the prevention of corrosion of metal surfaces.